The present invention relates to an image processing method and an image processing apparatus, and more specifically, to an image processing technology for suppressing artifacts generated in the magnification processing or the scaling of an image.
Images recorded on photographic film originals such as negative films, reversal films and the like are conventionally printed onto light-sensitive materials such as photographic papers and the like by so-called direct exposure, that is, a method in which an image on a film original is projected onto a light-sensitive material for areal exposure.
In contrast, there has been recently proposed a digital photoprint system which makes use of digital exposure. Briefly, the system photoelectrically reads image information recorded on a film, converts the thus read image into digital signals and thereafter subjects the digital signals to various steps of image processing to thereby provide image information for recording purposes; a latent image is recorded on a light-sensitive material by scan exposing it with recording light which has been modulated in accordance with the image information, and is then developed to produce a finished print. Digital photoprinters for embodying the above digital photoprint system are under development.
The digital photoprint system can freely perform editing and layouts jobs for print images such as composition of a plurality of images to a composite image, division of a single image into segments, editing of characters and images and the like and various types of image processing such as color/density adjustment, electronic magnification (scaling), edge sharpening (sharpness enhancement) and the like, and output finished prints which are freely subjected to editing and image processing in accordance with a specific use.
At the time, an image must be magnified (enlarged or reduced) in accordance with the size of an image to be output. Otherwise, the image is often reproduced with particularly a portion thereof being enlarged. In this case, electronic magnification processing is performed.
Further, image forming apparatuses such as digital copiers, facsimiles and the like also subject as required an image input with a scanner to magnification processing.
However, when the input image is enlarged or reduced, there has been conventionally arisen the following problem. That is, a sampling pitch in image inputting interferes with a re-sampling pitch in enlargement or reduction processing, which generates artifacts such as moirxc3xa9 and beats that are streaky irregularities.
To cope with this problem, for example, Japanese Unexamined Patent Publication No. 10-98612 discloses an image processing apparatus wherein a random coefficient, which is used for the enlargement and reduction of an image, is generated and the generated random coefficient is multiplied by a pixel value within a predetermined range including a pixel of interest in image data to be processed so as to form image data used for image enlargement or reduction, whereby the artifacts which are generated by the interference of the sampling pitch of a scanner with the re-sampling pitch in enlargement or reduction are suppressed.
However, the apparatus disclosed uses the random coefficient to diffuse the possibility of the artifacts and cannot perform processing in accordance with the frequency that the image has, which presents a problem that frequency characteristics cannot be realized. Then, when obtaining further reducing effects, it is difficult to obtain appropriate reducing effects of the artifacts in accordance with the image, no matter how the image is.
An object of the present invention, which was made in view of the above conventional problems, is to provide an image processing method capable of suppressing the artifacts that are generated in the magnification (enlargement and reduction) of an image. Another object of the invention is to provide an image processing apparatus for implementing the above method.
In order to attain the first object, the present invention provides an image processing method for performing magnification processing at a specified magnifying power, comprising the steps of:
dividing the magnification processing at the specified magnifying power into a first magnification processing step and a second magnification processing step; and
performing the first magnification processing step and the second magnification processing step,
wherein a start position of the first magnification processing step and a start position of the second magnification processing step are dislocated relatively to each other so that phases of pixel positions in the first and second magnification processing steps are reversed to each other.
Preferably, when the specified magnifying power is represented by s, the first and second magnification processing steps have magnifying powers represented by (s+1)/2 and 2s / (s+1), respectively.
Preferably, the magnifying power of the first magnification processing step is represented by (s+1)/2 and the magnifying power of the second magnification processing step is represented by 2s/(s+1).
Preferably, when the specified magnifying power is represented by s1 in a first direction and by s2 in a second direction perpendicular to the first direction, respectively, the first magnification processing step has a magnifying power in the first direction represented by (s1+1)/2 and a magnifying power in the second direction represented by (s2+1)/2, respectively, and the second magnification processing step has a magnifying power in the first direction represented by 2s1/(s1+1) and a magnifying power in the second direction represented by 2s2/(s2+1), respectively.
Preferably, the magnifying power s1 in the first direction is equal to the magnifying power s2 in the second direction.
Preferably, in the first and second magnification processing steps, the start position of the first magnification processing step and the start position of the second magnification processing step are dislocated relatively to each other in the first direction and the second direction perpendicular to the first direction.
Preferably, in the first and second magnification processing steps, the start position of the first magnification processing step and the start position of the second magnification processing step are dislocated relatively to each other by xc2xd of a pixel cycle in the first direction and the second direction perpendicular to the first direction.
Preferably, the start position of the second magnification processing step is dislocated by xc2xd of the pixel cycle with respect to the start position of the first magnification processing step in the first direction and the second direction perpendicular to the first direction.
Preferably, the magnification processing at the specified magnifying power is performed on a multi-level image.
In order to attain the second object, the present invention also provides an image processing apparatus for performing magnification processing at a specified magnifying power, comprising:
a device for performing a first magnification processing step;
a device for performing a second magnification processing step; and
a device for dislocating a start position of the first magnification processing step and a start position of the second magnification processing step relatively to each other so that phases of pixel positions in the first and second magnification processing steps are reversed to each other.
Preferably, when the specified magnifying power is represented by s, the first and second magnification processing steps have magnifying powers represented by (s+1)/2 and 2s/(s+1), respectively.
Preferably, the magnifying power of the first magnification processing step is represented by (s+1)/2 and the magnifying power of the second magnification processing step is represented by 2s/(s+1).
Preferably, when the specified magnifying power is represented by s1 in a first direction and by s2 in a second direction perpendicular to the first direction, respectively, the device for performing the first magnification processing step performs the magnification processing in which magnifying powers in the first and second directions are represented by (s1+1)/2 and (s2+1)/2, respectively, and the device for performing the second magnification processing step performs the magnification processing in which magnifying powers in the first and second directions are represented by 2s1/(s1+1) and 2s2/(s2+1), respectively.
Preferably, the magnifying power s1 in the first direction is equal to the magnifying power s2 in the second direction.
Preferably, the device for dislocating the start position of the first magnification processing step and the start position of the second magnification processing step is a device by which the start position of the first magnification processing step and the start position of the second magnification processing step are dislocated relatively to each other in the first direction and the second direction perpendicular to the first direction in the first and second magnification processing steps.
Preferably, the device for dislocating the start position of the first magnification processing step and the start position of the second magnification processing step is a device by which the start position of the first magnification processing step and the start position of the second magnification processing step are dislocated relatively to each other by xc2xd of a pixel cycle in the first direction and the second direction perpendicular to the first direction.
Preferably, the device for dislocating the start position of the first magnification processing step and the start position of the second magnification processing step dislocates the start position of the second magnification processing step by xc2xd of the pixel cycle with respect to the start position of the first magnification processing step in the first direction and the second direction.
Preferably, the magnification processing at the specified magnifying power is performed on a multi-level image.